public class code5 {
    //合并两个有序链表
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        ListNode newHead = new ListNode(-1);
        ListNode tmp = newHead;
        while(list1!=null&&list2!=null) {
            if(list1.val<list2.val) {
                tmp.next = list1;
                list1 = list1.next;
                tmp = tmp.next;
            } else {
                tmp.next = list2;
                list2 = list2.next;
                tmp = tmp.next;
            }
        }
        //用if不用while
        if(list1!=null) tmp.next = list1;
        if(list2!=null) tmp.next = list2;
        return newHead.next;
    }
}
